A11 - Potamogeton Pectinatus-Myriophyllum Spicatum Community

Summary

Synonymy

Slow-moving water community Tansley 1911; Submerged-leaf association Pallis 1911; Moderate current vegetation Butcher 1933; Submerged community Tansley 1939; Potamogeton filiformis-Chara sociation Spence 1964; Potametum pectinato-perfoliati Den Hartog & Segal 1964; Potamogeton perfoliatus Gesellschaft Oberdorfer 1977.

Constant species

Myriophyllum spicatum, Potamogeton pectinatus.

Rare species

Potamogeton filiformis, P. trichoides, Ranunculus baudotii.

Physiognomy

The Potamogeton pectinatus-Myriophyllum spicatum community includes most of the richer and more diverse pondweed vegetation in which Potamogeton pectinatus and Myriophyllum spicatum play a prominent role. Usually, both these plants are present, often in some abundance by mid-summer, but stands in which just one or the other occurs, together with the characteristic community associates, can also be placed here. P. pectinatus is particularly striking where the vegetation extends into more nutrient-rich, standing or slow-moving waters, where it can make rapid growth in early summer from its overwintering tuberous buds or fruits, forming bushy clumps up to 2 m or so long. M. spicatum can also grow luxuriantly in this community, and tends to perform rather better than P. pectinatus where the flow is somewhat faster or has occasional spates, so it is often the more abundant plant where the vegetation extends into the moderately swift reaches of rivers. M. alterniflorum, however, is very scarce here and only occurs where there is some influence from more basepoor and oligotrophic waters, where the community begins to grade to the Potamogeton-M. alterniflorum vegetation characteristic of such situations. The rare M. verticillatum occurs very locally in stiller waters, mostly in eastern England.

Other Potamogeton spp. occur with varying frequency and abundance in the community and further sampling might allow the definition of additional vegetation types of this general kind in which various of these pondweeds occur with more consistent prominence. Comparison with earlier accounts, however, suggests that local dominance among these associates was once much more widespread than is now the case (Pallis 1911, Tansley 1911, Pearsall 1921, Butcher 1933). P. pusillus, a linear-leaved pondweed like P. pectinatus, though not such a common plant, remains fairly frequent throughout,